The field of the invention is RC filters. More specifically the invention is related to an RC filter employing a fluid drop to form one of the capacitors. The gain vs. frequency curve of the RC filter is changeable by changing the fluid drop shape or composition. The RC filter can be used as a tunable RC filter, where the cut-off frequency can be tuned or as an analytical detector.
A resistor-capacitor (RC) circuit is an electronic circuit composed of resistors and capacitors. RC circuits can be used as RC filters when they are used to filter a signal by attenuating unwanted frequency elements of a specific signal. The gain vs. frequency curve of a RC filter typically is a function of the R (resistor) and C (capacitor) values.
A solid-fluid interface can act as a capacitor in the presence of an external electric field. If a fluid drop is placed on a dielectric surface such as Teflon, then that system can be modeled as a resistor-capacitor network and thus act as an RC filter. In such a system, the dielectric layer and the solid-fluid interface act as serially connected capacitors plus the fluid drop acts as a resistor connected in parallel to the latter capacitor. Adding an extra traditional resistor to this system results in a fluid drop based RC filter.
Electrowetting is the reduction of contact angle (making a surface more wettable by a liquid) by an applied voltage. Electrowetting on dielectric (EWOD) is when a thin dielectric layer is inserted between the electrode and the liquid to emulate the electric double layer in conventional electrowetting. The ideal dielectric blocks electron transfer, while sustaining the high electric field at the interface that results in charge redistribution when a potential is applied. When a hydrophobic dielectric is used, the large initial contact angle provides room for a large contact angle change upon electrowetting. Furthermore, by employing a dielectric layer between the liquid and electrode, virtually any kind of liquid can be used, regardless of the polarization of the interface.
Electrowetting on dielectric (EWOD) is now being accepted as one of the major ways for manipulating droplets in micro total analysis systems (μTAS) or lab-on-a-chip devices, where surface tension is one of the dominant forces. The advantages of a lab-on-a-chip device with electrowetting include negligible Joule heating, no moving micromechanical parts, and accurate and quick manipulation of droplets by digitally addressing of electrodes.
It would be useful to have an RC filter for which the cut-off frequency can be shifted within a tuning range and that can be tuned to a certain value according to the needs to achieve a particular purpose.
It would be useful to have a fluid drop based RC filter that can be used as a detector to detect an analyte in the fluid drop.